1. Field of the Invention
The present invention is related to a control apparatus and control method for an air conditioner employing two power sources, and particularly to a control apparatus and control method for an air conditioner for making the air conditioner operate continuously without any overstrain regardless of a momentary power failure in commercial A.C. power source.
2. Description of the Prior Art
Recently, there have been developed various kinds of electric appliances employing an additional independent power source utilizing solar heat as an energy source, besides commercial A.C. power source for the purpose of energy conservation. As a good example, an air conditioner employing two power sources is fully disclosed in Japanese patent laid-open publication No. 198648 (1992. 9. 20). The disclosed air conditioner adds D.C. power obtained from solar cells to another D.C. power converted from a commercial A.C. power source, converts the D.C. power into A.C. power with a variable frequency, and then drives a compressor motor with the converted A.C. power.
At this time, a possible damage of the compressor motor due to an overcurrent may be prevented by appropriately varying the frequency of the converted A.C. power in order that the current may not exceed a predetermined reference value.
On the other hand, there may frequently occur an irregularity in the commercial A.C. power source, such as a momentary power interruption or voltage drop. Such irregularity of the power source is usually restored within a short time such as tens of milliseconds.
Here, the compressor motor comes to a stop as soon as some irregularity occurs in the commercial A.C. power source, and assumes a re-starting mode the moment the irregularity of the commercial A.C. power source is eliminated.
At this time, a larger torque, that is, a larger current is required to re-start the compressor motor, because the pressure difference between the inlet and outlet of the compressor becomes great due to the operation before stoppage. As a result, the life span of the compressor may be shortened due to the large current.
To protect the compressor, the conventional air conditioner delays the re-starting action of the compressor motor until the pressure difference between the inlet and outlet of the compressor disappears. Such a delay time usually reaches up to three minutes, thereby resulting in a great nuisance to the user.